The ability to locate and track sounds in the three-dimensional world is essential for normal communication and navigation. When that ability is degraded, as with many types of hearing loss, communication is significantly disrupted. The long-term goal of this project is a complete understanding of the mechanisms and processes involved in human spatial hearing. Research conducted during previous funding periods has focused on issues related to the localization of single stationary sound sources in anechoic environments. Much has been learned from this research about the nature of the cues for sound direction and how those cues are used by human listeners. The research proposed in this application both extends and elaborates the earlier localization studies and moves into new areas such as the perception of sound source motion and the perception of source distance. The proposed methods include the virtual auditory space (VAS) technique, originally developed in the laboratory during previous funding periods, and a variant of the "conditioned-on-a-single-stimulus" (COSS) procedure, which can give quantitative estimates of the perceptual weight given by individual listeners to the various spatial cues. The new movement and distance studies will provide basic data on the discriminately and relative weighting of the various cues for movement and distance in several different stimulus conditions. The proposed localization experiments will address unanswered questions about processing of spectral cues and interaural delay cues and, in particular, about the relative weights assigned to these cues in different localization settings.